Question

Preciso muito dessa resolução!!!

Alternativas da Questão:
A)20
B)30
C)40
D)25
E)35

Answer 1

$\textbf{Dados:}$

$h_1=H;\ h_2=\dfrac{1}{3}H;\ v_2=20\ \mathrm{m/s};\ g\approx10\ \mathrm{m/s^2}$

$\mathbf{Resolu\c{c}\tilde{a}o}\textbf{:}$

$\Delta E=0\Longrightarrow U_1=U_2+K_2\Longrightarrow mgh_1=mgh_2+\dfrac{1}{2}mv_2^2$

$\Longrightarrow gH=g\left(\dfrac{1}{3}H\right)+\dfrac{1}{2}v_2^2\Longrightarrow \dfrac{2}{3}gH=\dfrac{1}{2}v_2^2\ \therefore\ \boxed{H=\dfrac{3}{4}\dfrac{v^2}{g}}$

$\Longrightarrow H=\dfrac{3}{4}\bigg(\dfrac{20^2}{10}\bigg)=\dfrac{3}{4}\bigg(\dfrac{400}{10}\bigg)=3(10)\ \therefore\ \boxed{H=30\ \mathrm{m}}$